This application claims the benefit of Japanese Application No. 2001-028705, filed Feb. 5, 2001, the entirety of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic component and a method for producing the same. The present invention is applicable to a dielectric resonator of a stacked type to be used for a resonance circuit, for example. The stacked type dielectric resonator is preferably used for a microwave band of several hundred MHz to several GHz.
2. Description of the Related Art
Recently, a noble metal powder which is used to prevent any structural defects caused in an electronic component and a heater has been suggested (see, for example, Japanese Laid-Open Patent Publication No. 8-7644). The noble metal powder is firstly prepared as a conductor paste. Then, the conductor paste is formed on a substrate (for example, ceramic green sheets). The substrate on which the conductor paste has been formed is sintered. Accordingly, an electrode is made from the conductor paste. That is, an electronic component or a heater in which the electrode is formed on the substrate can be made.
The surface of the noble metal powder is coated with a compound of metal and organic acid (metal salt of organic acid) and then heated in an inert atmosphere. When the conductor paste is prepared using the noble metal powder, the material far the noble metal powder and the material for the organic acid are selected and weighed out so that the percentage of firing shrinkage of the conductor paste is approximately the same as the percentage of faring shrinkage of the substrate (for example, ceramic green sheets).
When the conductor paste is formed on the substrate, and the conductor paste is thereafter sintered to produce an electronic component or a heater, then it is possible to avoid such a phenomenon that the electrode of the conductor paste is peeled off from the substrate or the electrode is evaporated, because the percentage of firing shrinkage of the conductor paste is approximately the same as that of the substrate. Thus, it is possible to prevent any structural defects which would otherwise occur in the electronic component or the heater.
When the conductor paste is prepared, the material for the noble metal powder and the material for the organic acid are selected and weighed out so that the percentage of firing shrinkage of the conductor paste is approximately the same as the percentage of firing shrinkage of the substrate. However, since the selection and the weighing-out operation for the materials as described above are extremely troublesome, the number of manufacturing steps may be increased.
Further, in conventional methods, the specific surface area of the noble metal powder is not considered at all. No consideration is made for the relationships among the specific surface area of the noble metal powder, the coating amount of the metal salt of organic acid, and the electric resistance value.
In other works, in order to prevent the occurrence of the structural defects, it is sometimes necessary to increase the coating amount of the metal salt of organic acid depending on the value of the specific surface area of the noble metal powder. In such a situation, the electric resistance value may be increased, and device characteristics and electric characteristics of the electronic component may be deteriorated.
An object of the present invention is to provide an electronic component and a method for producing the same which make it possible to reduce the occurrence of structural defects during and after the sintering of a dielectric substrate when an electrode is formed in the dielectric substrate.
An electronic component according to the present invention has a dielectric substrate and one or more electrodes. The dielectric substrate is formed by stacking a plurality of dielectric layers and sintering the plurality of stacked dielectric layers. The electrodes are formed of a paste, the paste contains metal powder particles, and each of the metal powder particles is coated with an inorganic oxide.
A method for producing an electronic component according to the present invention is applied to an electronic component having a dielectric substrate and one or more electrodes. That is, at first a plurality of dielectric layers is prepared. A paste is formed on one or more of the dielectric layers to form the electrodes of the paste. Subsequently, the plurality of dielectric layers are stacked and sintered. The paste contains metal powder particles, and each of the metal powder particles is coated with an inorganic oxide.
Usually, when the electrode is formed of a metal film, the shrinkage of the metal film is advanced faster than the shrinkage of the dielectric layer during the sintering which will be performed later. The reason for this is that the percentage of firing shrinkage of the metal film is greatly different from that of the dielectric layer. Therefore, delamination may be generated at a portion where the metal film has been formed. Residual stress may be also generated in the dielectric layer after the sintering. As a result, some structural defects may occur in the electronic component.
However, in the present invention, the electrode is formed by using the paste containing the material in which the metal powder particles are coated with the inorganic oxide. Therefore, no delamination is generated during the sintering, and no cracks are generated by the residual stress. That is, the percentage of firing shrinkage of the electrode is close to the percentage of firing shrinkage of the dielectric layer because of the coating of the inorganic oxide.
In the present invention, it is preferable that Ag is used for the metal powder particles. It is preferable that the BET specific surface area of the metal powder particle is 0.05 to 2 m2/g. If the BET specific surface area is less than 0.05 m2/g, the metal particles may become too large and pores may be formed in the electrode during the sintering. If the BET specific surface area is larger than 2 m2/g, it is necessary to increase the coating amount of the inorganic oxide in order to avoid the structural defects in the electronic component. As a result, the electric resistance of the electrode may be increased and the electric characteristics and the device characteristics may be deteriorated when the electronic component is completed. Therefore, it is preferable that the BET specific surface area of the metal powder particle is 0.05 to 2 m2/g.
According to the present invention, when the electronic component in which the electrodes are formed in the dielectric layer is produced, it is possible to reduce the occurrence of the structural defects in the electronic component during and after the sintering of the dielectric layer.
In the present invention, it is preferable that Ag is used for the metal powder particles. It is preferable that the BET specific surface area of the metal powder particle is 0.05 to 2 m2/g. If the BET specific surface area is less than 0.05 m2/g, the metal particles may become too large and pores may be formed in the electrode during the sintering. If the BET specific surface area is larger than 2 m2/g, it is necessary to increase the coating amount of the inorganic oxide in order to avoid the structural defects in the electronic component. As a result, the electric resistance as the electrode may be increased and the electric characteristics and the device characteristics may be deteriorated when the electronic component is completed. Therefore, it is preferable that the BET specific surface area of the metal powder particle is 0.05 to 2 m2/g.
It is preferable that the inorganic oxide is alumina. It is preferable that the metal powder particle is coated with the inorganic oxide in an amount of approximately 0.01 to 2% as converted into a value of oxide with respect to the metal powder particle.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.